Composition for sealant and pneumatic tire

Abstract

To provide a composition for a sealant which enables formation of a sealant layer that is excellent in shape retention property and sealing characteristics.SOLUTION: A composition for a sealant contains, with respect to 100 pts.mass of a solid rubber component containing 60 pts.mass or more of natural rubber, 95 to 150 pts.mass of a hydrocarbon resin containing 30 pts.mass or more of a terpene-based resin, and 20 to 100 pts.mass of a liquid plasticizer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composition for a sealant and a pneumatic tire using the same.

Background Art

[0002] As a pneumatic tire having a puncture prevention function, a tire in which a sealant layer is disposed on the inner surface of the tire is known. In a tire provided with a sealant layer, when a foreign object such as a nail pierces the tread and a through hole is formed, the sealant layer automatically closes the through hole to prevent air leakage from the tire. The sealant layer can be formed, for example, by discharging a composition for a sealant from a nozzle of a coating device and applying it to the inner surface of the tire.

[0003] As such a composition for a sealant, for example, Patent Document 1 describes a composition containing an unsaturated diene elastomer, a hydrocarbon resin between 30 phr and 90 phr, a liquid plasticizer between 0 phr and 60 phr having a Tg lower than -20°C, and a filler between 0 and less than 30 phr. However, the composition for a sealant described in Patent Document 1 has high viscosity at the application temperature, which places a load on the coating device, so it is necessary to suppress the application speed.

[0004] In order to improve the above-mentioned application speed, Patent Document 2 discloses increasing the content of the hydrocarbon resin. Specifically, 95 to 150 parts by mass of the hydrocarbon resin, 20 to 60 parts by mass of the liquid plasticizer, and a specific filler are blended with 100 parts by mass of the solid rubber component.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Tires with a sealant layer formed by a coating device are generally stored at room temperature in a stationary state. At that time, if the sealant layer is too soft, the sealant layer may flow and deform in a stationary state. Therefore, the sealant layer is required to have shape retention. On the other hand, when a foreign object such as a nail pierces the tread, the foreign object may be left pierced without being immediately pulled out. In that case, cracks may occur in the sealant layer over time, resulting in air leakage. Therefore, improvement of the sealing property against such air leakage over time is required.

[0007] In view of the above points, an embodiment of the present invention aims to provide a sealant composition capable of forming a sealant layer excellent in shape retention and sealing properties.

Means for Solving the Problems

[0008] The present invention includes the following embodiments. [1] A sealant composition comprising 95 to 150 parts by mass of a hydrocarbon resin containing 30 parts by mass or more of a terpene resin and 20 to 100 parts by mass of a liquid plasticizer with respect to 100 parts by mass of a solid rubber component containing 60 parts by mass or more of natural rubber. [2] The sealant composition according to [1], wherein the solid rubber component is a blend of natural rubber alone or at least one selected from the group consisting of polybutadiene, synthetic polyisoprene, butadiene copolymer, and isoprene copolymer and natural rubber. [3] The sealant composition according to [1] or [2], wherein the terpene resin contains a polyterpene resin. [4] The sealant composition according to any one of [1] to [3], wherein the liquid plasticizer contains an aromatic oil. [5] A pneumatic tire including a sealant layer formed of the sealant composition according to any one of [1] to [4].

Advantages of the Invention

[0009] According to the embodiment of the present invention, a sealant layer excellent in shape retention and sealing properties can be formed.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] As described above, the sealant composition according to the present embodiment contains a solid rubber component mainly composed of natural rubber, a hydrocarbon resin containing a terpene resin, and a liquid plasticizer, whereby a sealant layer excellent in shape retention and sealing properties can be formed. The mechanism is presumed as follows, although it is not limited thereto. Natural rubber is considered to have a cross-linked structure in which proteins and phospholipids are involved at the molecular terminals, and it is considered that a flow suppression effect is achieved by natural rubber occupying most of the matrix rubber. Further, in the hydrocarbon resin added as a plasticizing and adhesive component, by using a terpene resin having high compatibility with natural rubber, in combination with the high ratio of natural rubber in the solid rubber component, unevenness in the sealant composition is suppressed, and it is considered that the generation and growth of cracks over time are suppressed. Note that the sealing property refers to the performance of automatically closing through holes to prevent air leakage from the tire, and in the present embodiment, it refers to the performance of suppressing air leakage over time as described above.

[0012] In the present embodiment, 100 parts by mass of the solid rubber component contains 60 parts by mass or more, that is, 60 to 100 parts by mass of natural rubber (NR). It is preferable that 100 parts by mass of the solid rubber component contains 70 to 100 parts by mass of natural rubber, and more preferably 80 to 100 parts by mass. In this specification, "solid" means not having fluidity at 23°C.

[0013] The solid rubber component may contain other diene rubbers together with natural rubber, or may contain non-diene rubbers. Here, the diene rubber refers to a rubber having a repeating unit corresponding to a diene monomer having a conjugated double bond. Examples of other diene rubbers include synthetic polyisoprene (isoprene rubber; IR), polybutadiene (butadiene rubber; BR), isoprene copolymers, butadiene copolymers, and the like.

[0014] In one embodiment, the solid rubber component is preferably (a) natural rubber alone, or (b) a blend of at least one selected from the group consisting of polybutadiene, synthetic polyisoprene, butadiene copolymers, and isoprene copolymers and natural rubber. That is, 100 parts by mass of the solid rubber component preferably contains 60 to 100 parts by mass of natural rubber and 0 to 40 parts by mass of at least one selected from the group consisting of IR, BR, butadiene copolymers, and isoprene copolymers, and may contain 70 to 90 parts by mass of natural rubber and 10 to 30 parts by mass of at least one selected from the group consisting of IR, BR, butadiene copolymers, and isoprene copolymers.

[0015] Here, the butadiene copolymer is a copolymer of butadiene and other monomers, and examples thereof include styrene-butadiene rubber (SBR), butadiene-isoprene copolymer rubber, styrene-butadiene-isoprene copolymer rubber, and the like. The isoprene copolymer is a copolymer rubber of isoprene and other monomers, and examples thereof include styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-butadiene-isoprene copolymer rubber, and the like. For copolymer rubbers containing both butadiene and isoprene as monomers, they shall be included in the copolymer of the monomer having a higher molar ratio. That is, if the molar ratio of butadiene is higher than that of isoprene, it shall be included in the butadiene copolymer, and if the molar ratio of isoprene is higher than that of butadiene, it shall be included in the isoprene copolymer.

[0016] Examples of non-diene rubbers include butyl rubber, halogenated butyl rubber, ethylene propylene rubber, and the like.

[0017] Hydrocarbon resins are polymers essentially based on carbon and hydrogen. As the hydrocarbon resin, a solid thermoplastic resin having no fluidity at 23°C is preferably used. In the present embodiment, the hydrocarbon resin is compounded in an amount of 95 to 150 parts by mass with respect to 100 parts by mass of the solid rubber component. And, among the hydrocarbon resins compounded in an amount of 95 to 150 parts by mass, 30 parts by mass or more is a terpene resin.

[0018] The content of the hydrocarbon resin is preferably 95 to 130 parts by mass, more preferably 95 to 115 parts by mass, with respect to 100 parts by mass of the solid rubber component. When the content of the hydrocarbon resin is 95 parts by mass or more, the viscosity during coating can be lowered, making it easier to improve the coating speed. Also, it can prevent the sealant layer from becoming too hard at room temperature and improve the sealing properties. When the content of the hydrocarbon resin is 150 parts by mass or less, cracks are less likely to occur in the sealant layer, and the sealing properties can be improved.

[0019] The content of the terpene resin is 30 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 80 parts by mass or more, and still more preferably 95 parts by mass or more, with respect to 100 parts by mass of the solid rubber component as described above.

[0020] Terpene resins (terpene-based hydrocarbon resins) are resins obtained by polymerizing terpene compounds and have units derived from terpene compounds. Examples of terpene compounds include α-pinene, β-pinene, limonene, dipentene, and the like. Examples of terpene resins include polyterpene resins obtained by polymerizing only terpene compounds, and modified terpene resins obtained by polymerizing terpene compounds and monomers other than terpenes. Any one of these may be used, or two or more thereof may be used in combination. Examples of modified terpene resins include aromatic modified terpene resins (e.g., terpene-phenol resins) obtained by polymerizing terpene compounds and aromatic compounds.

[0021] As the terpene resin, it is preferable to use a polyterpene resin, and more preferably to use a pinene resin having α-pinene and / or β-pinene as the main monomer. It is preferable that 100% by mass of the terpene resin contains 50% by mass or more of the polyterpene resin, more preferably 80% by mass or more, and the polyterpene resin alone may be used.

[0022] The hydrocarbon resin may be a terpene resin alone, or a terpene resin and other hydrocarbon resins may be used in combination. The other terpene resins may be aliphatic, alicyclic, aromatic, or a combination thereof, for example, aliphatic / aromatic. Examples of the other hydrocarbon resins include petroleum resins and styrene resins.

[0023] The petroleum resin is a resin obtained by polymerizing a petroleum fraction. Examples include C5 aliphatic petroleum resins, C9 aromatic petroleum resins, and C5 / C9 aliphatic / aromatic copolymer petroleum resins. Any one of these may be used, or two or more thereof may be used in combination. The aliphatic petroleum resin is a resin obtained by polymerizing a petroleum fraction corresponding to 4 to 5 carbon atoms (C5 fraction), and may be hydrogenated. The aromatic petroleum resin is a resin obtained by polymerizing a petroleum fraction corresponding to 8 to 10 carbon atoms (C9 fraction), and may be hydrogenated. The aliphatic / aromatic copolymer petroleum resin is a resin obtained by copolymerizing a C5 fraction and a C9 fraction, and may be hydrogenated.

[0024] Styrene resins (styrene hydrocarbon resins) are resins obtained by polymerizing styrene monomers that are styrene or its derivatives (e.g., α-methylstyrene, vinyltoluene, 4-tert-butylstyrene, etc.), and may also be copolymers of styrene monomers and other aromatic monomers or aliphatic monomers. Examples of styrene resins include, for example, styrene / α-methylstyrene copolymers, α-methylstyrene homopolymers, styrene / aliphatic monomer copolymers, α-methylstyrene / aliphatic monomer copolymers, styrene / α-methylstyrene / aliphatic monomer copolymers, etc., and any one of these may be used or two or more thereof may be used in combination.

[0025] The softening point of the hydrocarbon resin is not particularly limited, but is preferably 80 to 150 °C, more preferably 80 to 130 °C. In this specification, the softening point is a value measured in accordance with ASTM D6090, and in the examples, it was taken as the value measured using "DP70" (automatic softening point measuring device) manufactured by Mettler Toledo.

[0026] The liquid plasticizer refers to a plasticizer that is liquid at 23 °C. That is, "liquid" means having fluidity at 23 °C. As the liquid plasticizer, it is preferable to use oil or liquid rubber, and oil and liquid rubber may be used in combination.

[0027] As the oil, various oils generally blended in rubber compositions can be used, and examples include mineral oil, vegetable oil, polyolefin oil, etc. Specific examples of preferred oils are mineral oils mainly composed of hydrocarbons, and examples include process oils such as paraffin oil, naphthene oil, and aromatic oil. Among these, it is preferable to use aromatic oil as the liquid plasticizer. Therefore, in one embodiment, 100% by mass of the liquid plasticizer preferably contains 50% by mass or more of aromatic oil, more preferably 80% by mass or more, and aromatic oil alone may be used.

[0028] As the aromatic oil, those having a mass percentage of aromatic hydrocarbons determined in accordance with ASTM D2140 of 15% by mass or more are preferable. That is, the process oil can contain aromatic hydrocarbons, paraffinic hydrocarbons, and naphthenic hydrocarbons in terms of its molecular structure, and those having a content ratio of the aromatic hydrocarbons of 15% by mass or more are preferably used, more preferably those of 17% by mass or more. The content ratio of the aromatic hydrocarbons is preferably 70% by mass or less, more preferably 65% by mass or less.

[0029] The liquid rubber is a rubber that is liquid at 23°C. Examples of the liquid rubber include liquid isoprene rubber, liquid butadiene rubber, liquid styrene-butadiene rubber, liquid isoprene-butadiene rubber, liquid isoprene-styrene rubber, liquid isoprene-butadiene-styrene rubber, liquid isobutylene, liquid ethylene-propylene-diene rubber (EPDM), and the like. These liquid rubbers may be those modified by carboxylation, methacrylation, or the like. Any one of these liquid rubbers may be used, or two or more thereof may be used in combination.

[0030] The weight average molecular weight (Mw) of the liquid rubber is not particularly limited, but is generally less than 100,000, and may be 1,000 to 80,000, or may be 2,000 to 60,000. The weight average molecular weight (Mw) of the diene rubber (including natural rubber) of the solid rubber component is generally 200,000 or more and is distinguished from the liquid rubber.

[0031] In this specification, the weight average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC). Specifically, for example, "HLC8320-GPC" manufactured by Tosoh Corporation equipped with a differential refractive index detector (RI) is used as a measuring device, tetrahydrofuran (THF) is used as a solvent, "TSKgel SuperHZM-M" manufactured by Tosoh Corporation is used as a column, the measurement temperature is 40°C, the flow rate is 0.35 mL / min, the concentration is 1.0 g / L, the injection volume is 40 μL, and it is calculated in terms of polystyrene using commercially available standard polystyrene.

[0032] The content of the liquid plasticizer is 20 to 100 parts by mass, preferably 30 to 80 parts by mass, more preferably 35 to 80 parts by mass, and still more preferably 45 to 70 parts by mass with respect to 100 parts by mass of the solid rubber component. When the content of the liquid plasticizer is 20 parts by mass or more, the viscosity during coating can be lowered, facilitating an improvement in the coating speed, and the sealing properties in the sealant layer can be improved. When the content of the liquid plasticizer is 100 parts by mass or less, it becomes easier to ensure the shape retention of the sealant layer.

[0033] In addition to the above components, various additives such as a filler, zinc oxide, stearic acid, processing aid, softening agent, wax, anti-aging agent, crosslinking agent, and vulcanization accelerator may be appropriately blended within a normal range in the sealant composition according to this embodiment. In one embodiment, it is preferable that the sealant composition does not contain a crosslinking agent and a vulcanization accelerator. Here, sulfur may be mentioned as the crosslinking agent. Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, guanidine-based, thiuram-based, and thiazole-based vulcanization accelerators.

[0034] Examples of the filler include carbon black and / or silica. The carbon black is not particularly limited, and various known varieties can be used. The silica is also not particularly limited, and examples thereof include wet silica such as wet precipitation method silica and wet gelation method silica. The content of the filler is not particularly limited, and for example, it may contain 0 to 30 parts by mass, or may contain 0 to 20 parts by mass with respect to 100 parts by mass of the solid rubber component. In one embodiment, the sealant composition may not contain a filler, or may contain a small amount of carbon black for coloring purposes, for example, 0.5 to 8 parts by mass with respect to 100 parts by mass of the solid rubber component.

[0035] The sealant composition according to this embodiment can be produced by kneading in accordance with a conventional method using a kneader commonly used in the rubber industry. For example, in the first step, a compounding agent excluding the hydrocarbon resin is added to and kneaded with the solid rubber component. Next, in the second step, the hydrocarbon resin is added and kneaded. Thereby, the sealant composition is obtained.

[0036] In the first step, for example, a kneader such as a Banbury mixer, a roll mill, or a kneading extruder is used. In the first step, a liquid plasticizer is charged into the kneader together with the solid rubber component, and further compounding agents excluding the hydrocarbon resin are optionally added, and kneading is performed while raising the temperature of the kneaded product. The discharge temperature of the kneaded product from the kneader in the first step is not particularly limited, but may be, for example, 120 to 160°C.

[0037] In the second step, for example, a kneading extruder such as a twin-screw kneading extruder or a conical kneader is used. In the second step, the hydrocarbon resin is charged into the kneading extruder together with the kneaded product obtained in the first step and kneaded. The discharge temperature of the kneaded product from the kneader in the second step is not particularly limited, but it is preferably a temperature higher than the softening point of the hydrocarbon resin. Thereby, the dispersibility of the hydrocarbon resin can be improved. The discharge temperature in the second step is preferably 80 to 160°C, more preferably 100 to 160°C.

[0038] The sealant composition according to this embodiment can be used to form a sealant layer on the inner surface of a pneumatic tire. Examples of the pneumatic tire include pneumatic tires of various applications and various sizes, such as passenger car tires and heavy-duty tires used for trucks and buses.

[0039] An embodiment of a pneumatic tire having a sealant layer will be described with reference to FIG. 1. The pneumatic tire 1 includes an annular tread 2 that contacts the road surface, a pair of left and right bead portions 3, 3 located inside the tread 2 in the tire radial direction RD, and a pair of left and right sidewalls 4, 4 located between the tread 2 and the bead portions 3, 3. The tire 1 includes a bead core 5 embedded in the bead portion 3, a carcass ply 6 extending toroidally between the left and right bead portions 3, 3, a belt 7 and a tread rubber 8 provided on the outer peripheral side of the carcass ply 6 in the tread 2, an inner liner 9 provided on the inner surface side of the carcass ply 6, and a sealant layer 10 provided on the inner surface side of the inner liner 9.

[0040] The sealant layer 10 is provided by being overlaid on the inner surface 1A of the pneumatic tire 1, specifically, on the inner side of the inner liner 9. In this example, the sealant layer 10 is provided from one end to the other end in the tire axial direction AD on the inner surface 1A of the tread 2. In this way, it is preferable that the sealant layer 10 is provided over the entire inner surface of the tread 2, and it may be provided only on the inner surface of the tread 2, or it may be provided in a wider range including the inner surface of the tread 2. That is, the sealant layer 10 is preferably provided on the inner surface 1A of the tire 1 including the inner surface of the tread 2.

[0041] The method for forming the sealant layer is not particularly limited, but preferably, the sealant composition is heated to a temperature higher than the softening point of the hydrocarbon resin (for example, 80 to 160 °C) and applied to the inner surface of the pneumatic tire using an application device. Specifically, for example, the sealant composition may be discharged in a strip shape from the nozzle of the application device and applied along the tire circumferential direction while displacing the strip in the tire axial direction with respect to the tire inner surface. After application, by leaving it at room temperature, the fluidity of the sealant composition decreases and it adheres to the inner surface of the pneumatic tire, thereby forming the sealant layer.

[0042] The thickness of the sealant layer is not particularly limited, and may be, for example, 3 to 7 mm.

Examples

[0043] Examples are shown below, but the present invention is not limited to these examples.

[0044] Each component used in the examples and comparative examples is as follows. ·NR: RSS#3 ·IR: "IR2200" manufactured by JSR Corporation ·BR: "UBEPOL BR150B" manufactured by UBE Industries, Ltd. · Aroma oil: "Process NC140" manufactured by ENEOS Corporation · Petroleum resin 1: Aliphatic / aromatic petroleum resin, "Petrotac 90" manufactured by Tosoh Corporation, softening point = 95°C · Petroleum resin 2: Aliphatic / aromatic petroleum resin, "PR-373" manufactured by ExxonMobil, softening point = 96°C · Politerpene resin 1: Pinene resin, "Sylvataxx 4125" manufactured by KRATON, softening point = 125°C · Politerpene resin 2: Pinene resin, "Sylvataxx 4150" manufactured by KRATON, softening point = 115°C · Politerpene resin 3: Pinene resin, "Sylvataxx 8125" manufactured by KRATON, softening point = 124°C · Styrene resin 1: α-Methylstyrene resin, "Sylvataxx 4401" manufactured by KRATON, softening point = 85°C · Styrene resin 2: α-Methylstyrene resin, "Sylvataxx 4412" manufactured by KRATON, softening point = 138°C

[0045] [Examples 1 to 10, Comparative Examples 1 to 9] Sealant compositions of Examples 1 to 10 and Comparative Examples 1 to 9 were prepared according to the formulations (parts by mass) shown in Table 1 below. Specifically, first, in the first step, components excluding the hydrocarbon resin were kneaded using a Banbury mixer (discharge temperature 145°C). Then, in the second step, a twin-screw kneading extruder was used to add and knead the hydrocarbon resin to the kneaded product obtained in the first step (discharge temperature 140°C) to obtain a sealant composition.

[0046] For each of the obtained sealant compositions, the shape retention of the sealant layer and the sealing properties were evaluated. The evaluation methods are as follows.

[0047] (1) Shape retention: After heating the sealant composition to 150°C using a material coating system manufactured by Nordson, 4.0×10 5While discharging from the nozzle at a pressure of Pa, it was applied to the inner surface of a pneumatic tire (tire size: 215 / 55R17) to form a sealant layer with a thickness of 4 mm. After stacking the pneumatic tires with the sealant layer formed at room temperature and storing them statically for 2 weeks, the inner surface of the tire was observed to confirm whether the sealant layer had undergone flow deformation. Those that did not undergo flow deformation were marked with "○" (good shape retention), and those that underwent flow deformation were marked with "×" (poor shape retention).

[0048] (2) Sealing characteristics: Using a pneumatic tire equipped with a sealant layer prepared in the same manner as the evaluation of the above shape retention, the tire was mounted on a rim and filled with air at an internal pressure of 180 kPa. A nail (diameter 5.2 mm, length 50 mm) was passed through the tread and left stationary for 1 week as it was, and then the sealing characteristics were evaluated based on whether there was air leakage. Those with a decrease in internal pressure of less than 5% were marked with "○" (good sealing characteristics), and those with a decrease in internal pressure of 5% or more were marked with "×" (poor sealing characteristics).

[0049]

Table 1

[0050] The results are as shown in Table 1. In Comparative Example 1, since the amount of NR was less than the specified amount, and in Comparative Example 2, since IR was used instead of NR, the sealant layer had undergone flow deformation during static storage and was inferior in shape retention.

[0051] In Comparative Examples 3 to 5, since NR was contained in an amount equal to or more than the specified amount as the solid rubber component, although they were excellent in shape retention, they were inferior in sealing characteristics because terpene resin was not used as the hydrocarbon resin.

[0052] In Comparative Example 6, since the amount of terpene resin was less than the specified amount, the sealant layer was hard at room temperature and was inferior in sealing characteristics. In Comparative Example 7, since the amount of terpene resin was more than the specified amount, cracks occurred in the sealant layer and it was inferior in sealing characteristics.

[0053] In Comparative Example 8, since the liquid plasticizer was not included, the sealant layer was hard at room temperature and had poor sealing properties. In Comparative Example 9, since the liquid plasticizer was more than the specified amount, the shape retention of the sealant layer was poor.

[0054] On the other hand, in Examples 1 to 10, since the solid rubber component contained NR within the specified amount and a terpene resin was blended as the hydrocarbon resin, the shape retention was excellent, and the generation and growth of cracks due to the passage of time in the nail driving test were suppressed, and the sealing properties were excellent.

[0055] Note that various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all of these combinations are described in the specification as preferred numerical ranges. Also, the description of the numerical range of "X to Y" means X or more and Y or less.

Explanation of Signs

[0056] 1... pneumatic tire, 2... tread, 3... bead part, 4... sidewall, 5... bead core, 6... carcass ply, 7... belt, 8... tread rubber, 9... inner liner, 10... sealant layer

Claims

1. Based on 100 parts by mass of a solid rubber component containing 60 parts by mass or more of natural rubber, 95 to 150 parts by mass of a hydrocarbon resin containing 30 parts by mass or more of a terpene resin, 20 to 100 parts by mass of a liquid plasticizer, A composition for a sealant containing the above.

2. The solid rubber component is natural rubber alone, or a blend of at least one selected from the group consisting of polybutadiene, synthetic polyisoprene, butadiene copolymer, and isoprene copolymer and natural rubber, The composition for a sealant according to Claim 1.

3. The composition for a sealant according to Claim 1, wherein the terpene resin contains a polyterpene resin.

4. The composition for a sealant according to Claim 1, wherein the liquid plasticizer contains an aromatic oil.

5. A pneumatic tire provided with a sealant layer formed of the composition for a sealant according to any one of Claims 1 to 4.

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